Inflammatory Bowel Disease encompasses two principal conditions: ulcerative colitis (UC) and Crohn's disease (CD). Some patients have features of both subtypes and are classified as IBD-undefined (IBD-U) (Gastroenterology, 2007. 133(5): p. 1670-89). UC is defined by continuous mucosal inflammation starting in the rectum and restricted to the colon while CD inflammation can occur anywhere in the gastrointestinal tract, involves full thickness of the bowel wall and often with skip lesions (Gastroenterol Clin North Am, 2009. 38(4): p. 611-28; Gastroenterology, 2007. 133(5): p. 1670-89). Recent attempts to find new markers for IBD subtypes, such as conventional antibodies, have fared very poorly at differentiating colonic CD versus UC. As treatments and responses to medical therapies differ between CD and UC (J Pediatr Gastroenterol Nutr, 2010, S1-S13. The American journal of gastroenterology, 2011. 106 Suppl 1: p. S2-25; quiz S26. Gastroenterol Clin North Am, 2009. 38(4): p. 611-28) there is an urgent need for biomarkers to differentiate between CD and UC.
The primary tool used for both diagnosis and IBD management is endoscopy (World J Gastrointest Endosc, 2012. 4(6): p. 201-11). Endoscopy enables both visualization of the mucosa and access for mucosal biopsies to diagnose disease, to define disease extent and activity, and to monitor disease progression. The diagnostic accuracy from colonoscopy ranges from 60 to 74% (J Clin Pathol, 2002. 55: p. 955-60). Other diagnostic approaches include radiological imaging and histological examination of mucosal biopsies in the differentiation of IBD subtypes (e.g non-caseating submucosal granuloma). However, 10% of patients (Registry. Dtsch Arztebl Int 2015; 112:121-7) have ambiguous diagnosis using these approaches and are instead classified as IBD-unclassified (IBD-U) patients (J Pediatr Gastroenterol Nutr 2014; 58:795-806). Accurate and early diagnosis is essential for proper disease management. The goal of IBD treatment is to bring active disease into remission and to prevent follow-up relapse (flare-ups). The choice of treatment depends on disease subtype (CD versus UC), disease location, severity of disease, disease complications and individual host factors (e.g. nutritional and growth status, pubertal status, child's age and size, medication allergies) (J Pediatr Gastroenterol Nutr, 2010, S1-S13. The American journal of gastroenterology, 2011. 106 Suppl 1: p. S2-25; quiz S26. Gastroenterol Clin North Am, 2009. 38(4): p. 611-28). Current drug therapies consist of aminosalycylates, immune-modulators, corticosteroids, antibiotics and biological therapies (i.e. anti-TNFα monoclonal antibodies). The optimum therapeutic regimen for maintaining a disease free state still remains to be determined and the effectiveness of these drugs significantly differs between CD and UC (J Pediatr Gastroenterol Nutr, 2010, S1-S13. The American journal of gastroenterology, 2011. 106 Suppl 1: p. S2-25; quiz S26. Gastroenterol Clin North Am, 2009. 38(4): p. 611-28). For example, 5-aminosalicylic acid (5-ASA) drugs are moderately effective at inducing remission and preventing relapse in mild-to-moderate-active UC, while they are not recommended in the management of active CD (The American journal of gastroenterology, 2011. 106 Suppl 1: p. S2-25; quiz S26). There is good evidence for use of methotrexate as maintenance therapy to prevent relapse in CD however, there is no evidence for its use in UC (The American journal of gastroenterology, 2011. 106 Suppl 1: p. S2-25; quiz S26). Greater doses of anti-TNFα therapies at more frequent intervals are being just now recognized to be required for successful treatment of severe UC as compared to standard treatment protocols in use for CD. One third of the cost associated with IBD is due to medical therapies (CCFC. 2008, report. p. 1-101) stressing the economic importance of an effective treatment and thereby an accurate diagnosis.
Genome wide association studies in both adults and pediatric patients have identified novel IBD-associated genes but only define 25% of the genetic risk for developing IBD and excepting for very young infants (i.e. <2 years of age), no unique genes have been discovered that define pediatric IBD from adult-onset IBD. IBD is a complex polygenic disease involving multiple risk gene loci (Nature genetics, 2008. 40(8): p. 955-62. Nature genetics, 2009. 41(12): p. 1335-40. Nature genetics, 2010. 42(4): p. 332-7). These loci encode genes involved in innate and adaptive immunity, autophagy, and maintenance of epithelial barrier integrity for those genes that have known function. While these studies have shown us that multiple pathways are involved in the pathogenesis of IBD, we remain surprisingly ignorant on the root cause(s) and pathogenesis of IBD.
Protein biomarkers could complement current IBD diagnostic tools by reducing ambiguous diagnosis of IBD, subtype differentiation and may also deliver insight into the disease course. Previous studies have identified proteins that are elevated and measurable in serum or stool, however the clinical relevance of these proteins in diagnosis of IBD-U patients is limited, and have been found to perform best in more obvious cases of CD or UC in the pediatric population (Pediatrics 2010; 125:1230-6; Inflamm Bowel Dis 2012; 18:1493-7). Serum detected antibodies directed against neutrophil or bacterial components tend to have low sensitivities (true positive rate <50%). Other biomarkers are now becoming available, namely fecal calprotectin, which are clinically useful to identify IBD patients from populations without mucosal inflammation (e.g. irritable bowel syndrome (IBS), healthy controls), but cannot differentiate IBD subtypes (A mini-review. Can J Gastroenterol Hepatol 2015; 29:157-63). Fecal calprotectin has not proven to be a good measure to distinguish between mild, moderate or severe disease (Inflamm Bowel Dis 2012; 18:1493-7) which is important in deciding appropriate therapeutic intervention. There is a clear need for new approaches that can rapidly and accurately provide an early diagnosis of IBD, particularly considering the lack of good genetic and protein markers, atypical presentations and the often rapid progression of IBD in the pediatric population.
In view of the above there is a need for better diagnostic methods.